1. Field of Invention
This invention relates to an integrated circuit (IC) manufacturing process, and more particularly to a method of controlling the statuses of a plurality of wafers in an IC manufacturing process.
2. Description of Related Art
Because a current IC manufacturing process includes numerous steps, the status of each wafer has to be monitored at every moment for a higher yield. For example, an originally flat wafer is warped upward or downward after a film causing a tensile or compressive stress is formed thereon, after a high-temperature process is conducted thereto or after a film thereon is removed by CMP or other method. After numerous processes affecting the degree of warp are conducted, the progressive upward or downward warp of the wafer could be overly large, especially as the diameter of a wafer is larger than 8 inches.
Warp of a wafer can be detected, for example, in a physical vapor deposition (PVD) process that uses a ring-shaped clamp contacting the edge of the wafer and a backside gas supplied into a table under the wafer to fix the wafer on the table. If the wafer is warped, the backside gas would exit from under the wafer to greatly increase-the-pressure detected in the chamber.
When the warpage of a wafer is overly large, cracks may occur to the edge of the wafer when a ring-shaped clamp is used to fix the wafer on a table or when a claw-like clamp is used to hold the wafer, and the cracks easily extend in subsequent processes to significantly damage the dies. Moreover, an overly warped wafer cannot be stably fixed on an electrostatic chuck, for an electrostatic chuck can merely contact with a central portion of an upward warped wafer or an edge portion of a downward warped wafer. In addition, when a wafer is overly warped, the patterns on a photomask cannot be transferred accurately onto a photoresist layer coated on the warped wafer.
Accordingly, it is an important issue to control the warpage of a wafer, especially when the diameter of the wafer is larger than 8 inches.